In recent years, an improvement in performances of a thin film magnetic head has been demanded with an improvement in areal recording density of a hard disk apparatus. As the thin film magnetic head, there has been widely used a composite type thin film magnetic head having a configuration in which a recording head having an induced magnetic conversion element for writing and a reproducing head having a magneto-resistive (which will be referred to as MR hereinafter) element for reading are superimposed. As the MR element, a GMR element using a giant magneto-resistive (which will be referred to as GMR hereinafter) effect such as a spin valve film structure (which will be referred to as an SV film structure) or a ferromagnetic tunneling magneto-resistive element (which will be referred to as a TMR element hereinafter) forms a current main stream.
As a method of improving performances of a reproducing head, there is, e.g., a method which adapts a pattern width of a GMR film, especially an MR height. This MR height means a length (a height) from an end portion of the GMR element on an air bearing surface (which will be referred to as ABS hereinafter) side to an end portion of the same on the opposite side, and is controlled based on a polishing quantity when machining the ABS. It is to be noted that the ABS used herein is a surface facing a magnetic disk of a thin film magnetic head and also referred to as a track surface.
On the other hand, with an improvement in performances of a reproducing head, an improvement in performances of a recording head has been also demanded. As a factor which determines performances of a recording head, there is a throat height (TH). The throat height means a length (a height) of a pole portion from the ABS to an edge of an insulating film which electrically insulates a thin film coil for magnetic flux generation. In order to improve performances of a recording head, a reduction in throat height has been demanded. This throat height is also controlled based on a polishing quantity when machining the ABS.
Of performances of a recording head, a track density in a magnetic disk must be improved in order to enhance a recording density. In order to realize this, there is a need to realize a recording head having a narrow track structure in which widths of a lower pole portion (a bottom pole) and an upper pole portion (a top pole) formed with a write gap therebetween in the ABS are reduced on the order of several microns to submicron.
However, simply reducing a track width is not enough, and an intensive recording magnetic field must be generated and sufficient overwrite characteristics must be assured even when a track width is reduced.
In order to generate a sufficiently intensive magnetic recording field, approximating a flare point, where a track width is narrowed down to a predetermined width, to the ABS is effective. However, an intensity of a magnetostatic leakage field is also increased when this technique is used. A magnetostatic leakage field provokes a problem of erasing recorded information of an adjacent track. Therefore, approximating a flare point to the ABS in order to increase an intensity of a recording magnetic field is not necessarily easy. Further, when a flare point is approximated to the ABS, since a change in characteristics becomes large, instability and irregularities are apt to occur.
JP 2000-105907A (Reference 1) discloses a thin film magnetic head which enables a correct control over a pole portion width and obtains sufficient overwrite characteristics even if the pole portion width is reduced. As its concrete configuration, an upper pole portion is divided into a pole rear portion which is continuous with a yoke portion and a pole end portion which is narrower than the pole rear portion, and a track width is defined by the pole end portion. A position of a portion where the pole rear portion is coupled with the pole end portion is matched with a throat height zero position (a TH0 position) which is a reference for a throat height TH, and a widthwise direction step which varies at substantially right angles is provided here. A width of the pole rear portion in this coupling portion is set to be sufficiently larger than a width of the pole end portion in the coupling portion.
According to the conventional configuration mentioned above, expansion of a pattern width of a photo resist which is used to form the pole end portion can be avoided, and a write track width can be minimized. Furthermore, existence of the pole rear portion with a large width can prevent a magnetic flux generated in the yoke portion from being saturated before reaching the pole end portion, thereby assuring the sufficient overwrite characteristics.
However, since the overwrite characteristics are dependent on existence of the pole rear portion, a problem of a change in the overwrite characteristics due to a pattern fluctuation of the pole rear portion is involved in the thin film magnetic head disclosed in Reference 1. Reference 1 does not disclose a countermeasure for this problem.